1. Field of the Invention
This invention pertains generally to the application of a drawing lubricant to the surface or surfaces of metallic sheet material, and more particularly to the application of a uniform coating resulting in a dry film of the drawing lubricant on the surface or surfaces.
2. Description of the Prior Art
Forming of metal parts by stamping or drawing metal sheets in many instances requires the presence of a lubricating film on the surface or surfaces of the sheets. Such lubricants were initially conventionally applied in liquid form by dipping blanks or continuous coil stock in a bath of the lubricant. This procedure has not proven entirely satisfactory in that it is time and labor consuming and often results in application of uneven coatings. The coated blanks or stock, inasmuch as the coating material remains in liquid form, are messy to handle and tend to create unpleasant, foul conditions throughout the working area and around the equipment within which they are fabricated and processed.
More recently, so-called dry-film lubricants have been employed wherein the film material is applied in a liquid or wet state, and then processed to a dry state prior to the actual metal forming operation. Such dry film lubricants are required for the more difficult drawing operations which require retention of the lubricating film through subsequent stages of the drawing process. They are available in both solid and liquid form. The solid form lubricant is heated to liquify it to permit application by conventional coating methods, and then cooled to again solidify. The liquid form lubricant, following application by traditional liquid coating techniques, is heated to insure removal of a majority of its liquid content in order to achieve a dry film. Drying of the liquid coating normally involves transporting the coated blanks on a conveyor line past heaters to accelerate evaporation of the liquid. A considerable amount of space is required for the conveyor system and heaters used in moving parts past the heaters, and excessive labor may be required for loading and unloading the conveyor as well as for transporting coated blanks to various press working locations throughout a plant.
There is disclosed in U.S. Pat. No. 2,614,526 a metal stock oiler comprising a sump, an upper tube and a lower tube each having perforations therein for spraying lubricant on both surfaces of the stock, and a pump for forcing the lubricant out through the apertures. Baffles are provided above and below the stock for confining lubricant within the device, and the stock passes between rollers after the lubricant is sprayed on its surfaces.
U.S. Pat. No. 2,966,425 discloses apparatus for applying metal working lubricants, and particularly dry lubricants, to sheet metal. The sheet passes between rubber rolls, each of which has an associated steel doctor roll. Pipes apply the coating composition to the rubber coating rolls in advance of its convergence with the doctor roll. Following coating, the sheet passes through a drying apparatus. U.S. Pat. Nos. 4,147,126 and 4,384,544 pertain to systems for applying a liquid coating simultaneously to both surfaces of a continuous web of material using a roller transfer procedure.